1. Technical Field
This invention relates to a hammer mill for processing recycled glass provided with two separate grinding stages operating simultaneously on dissimilar rotors with an improved separation loop utilizing vacuum pressure and paper shredders for enhanced particle flow and separation resulting in improved product.
2. Background
Single stage hammer mills are well known. In hammer mills, the product to be ground is subjected to flailing motion from a large number of hammers or blades carried on a central rotor. A major drawback in such mills is the imprecise control over the grinding process. Another major drawback is the inability of hammer mills to remove the paper from the final product.
Typically in single stage hammer mills, in order to obtain finely ground product, it is necessary to employ finely meshed screens. Screens, particularly those employing fine meshes, have several drawbacks. One drawback is that screens slow the rate of material flow, reducing throughput. Another drawback is that fine mesh screens are susceptible to clogging from foreign materials and particles, particularly paper.
Hammer mill systems in general are often incapable or highly inefficient at producing both fine and coarsely-ground materials. As a result, different machines must be used to grind different coarsenesses. Thus, these machines tend to be specialized and do not perform efficiently across wide ranges of grinding coarsenesses.
Another drawback of both single stage and double stage hammer mills which affects the rate of flow through the machine is air flow. Typically, finely-ground material must be entrained in an air flow stream and exhibits a tendency to pile up in corners and "dead spots" within the system. The problem of maintaining high velocity flow in a system incorporating fine mesh screens has been one which has eluded the prior art.
Another drawback of single and double stage hammer mills is the relatively poor control over aggregate particle sizes produced. Typically in the case of a double stage hammer mill, raw material makes one pass through the hammer mill, receiving a coarse grinding followed by a fine grinding and is then separated. In a single stage hammer mill, material typically makes one pass through the system, receiving only a coarse grinding. Such systems provide for very poor control over the aggregate product size. Thus, typical single stage and double stage hammer mills are inefficient at producing specific aggregate output size and must be designed with limited ranges in mind. What is needed is a hammer mill which is capable of controllably producing product within tighter grit ranges over a wider range of aggregate sizes which may be easily reconfigured to produce different aggregate sizes.
Efficiency is another drawback to single and double stage hammer mills. Single and double stage hammer mills of the prior art typically have minimal control over aggregate output size, and thus are highly inefficient at producing quantities of specific aggregate product size. What is needed is a hammer mill that is capable of producing specific aggregate output size that is controllable over finite ranges which may also be easily reconfigured to efficiently produce different aggregate particle sizes.
It is an objective of the present invention to overcome these various disadvantages and to provide other advantages in a hammer mill having two stages consisting of a coarse-grind followed by a fine grind. It is another objective of the present invention to provide a dual hammer mill system which is capable of operating continuously and automatically conveying the semi-ground and ground product from the first stage to the second stage, then through a separation loop and into collection containers. It is a further objective to provide in such a continuous system for greater throughput and tighter control over aggregate product size.
A further objective of the invention is to provide a two stage hammer mill wherein the semi-ground product is moved from the first stage to the second stage and through the separation loop by a combination of gravity and pneumatic pressure.
A further objective of the invention is to provide a two stage hammer mill in which the second stage is capable of producing sufficient air velocity to continually draw material through the first stage and entrain the semi-ground product, which is then introduced into the second stage hammer mill for continuous grinding until it is drawn through adjustable gate means which regulate material flow to the separation loop. More particularly, it is an objective of the present invention to provide a two stage hammer mill having the foregoing advantages and in which the semi-ground product exiting from the second stage hammer mill is controllably drawn into a separation loop for more precise control over the aggregate particle size of the finished product. It is a further objective to provide such a separation loop utilizing vacuum pressure means for removing paper, dust, and other fine materials and collecting them as waste, while reducing the overall dust level associated with such a device. A further objective is to increase through put by providing a removable shaker screen for easily removing cloggages.
It is a further objective of the present invention to provide a two stage hammer mill having the foregoing advantages which is particularly adapted for precise control over the ground product size, and in such a system whereby precise control over product size can be easily changed.